Which Harry Potter book was the first to sell more than one million copies in its first week in the United Kingdom?

Harry Potter and the Goblet of Fire was the first Harry Potter book to sell more than one million copies in its first week in the United Kingdom.

Published on 8 July 2000, the fourth novel sold more than 372,000 copies in Britain on its first day and passed one million copies during its first week. Those figures made its launch a major publishing event rather than an ordinary children’s-book release.

The novel is also notable within the story because it introduces the Triwizard Tournament, a dangerous international magical competition hosted at Hogwarts. Harry is unexpectedly entered as a fourth champion despite being under the required age.

Later books broke additional sales records. Harry Potter and the Order of the Phoenix sold more than five million copies in its first 24 hours in the United States, so different records belong to different volumes.